1. Field of the Invention
The invention concerns data integrity in applications employing smartcards.
2. Prior Art
Secure smartcards today find application in a number of different functions and are being used in increasing numbers. To some extent the data on the smartcard may be of considerable value, such as-means of payment payment limits or personal (e.g. medical) data. Data protection legislation and the fact that it is a smartcard personal data store make it difficult to provide data security. For these reasons the highest demands are made on the integrity of the data on a smartcard. With the anticipated large numbers in the expansion of smartcards even low error rates can lead to a considerable number of errors.
The expression integrity of data means freedom from errors in the sense that they retain the information entered on them as an accurate picture of the reality and can therefore be used for meaningful data processing. Correspondingly consistency of the data signifies agreement of the data with the reality which they represent. For this both a formal (physical condition) and a contextual (semantic functional) requirement must be fulfilled.
The integrity of the data on a smartcard is endangered particularly by physical influences both on the smartcard as such and also during a reading operation.
The most used smartcards implement the ISO standard 7816-X or the analogous national standards. In accordance with these data on the smartcard is organized in files. Parts of a file can be written as records or as any Sequence of symbols with write commands. Errors which appear in the smartcards during the writing process will be notified to the read-write equipment. If, for mechanical, electrical or electronic reasons, the writing process is not terminated and the read-write equipment and/or the smartcard cannot undertake any error correction, the data is inconsistent.
In particular, smartcards are ever more frequently employed in conjunction with non-motorized smartcard readers. Especially with these cheap readers, in which the insertion and removal of the smartcard is effected manually, the user of the smartcard can abort the process by removing the smartcard prematurely. In addition external influences such as vibration or power failure can lead to such abortions of the current use. The consequence of this may be that the aborted application leaves inconsistent data conditions on the smartcard and in the smartcard reader which makes the smartcard unusable for further application.
Two functions are for example incorporated on a smartcard: an electronic wallet and an authority to visit a fitness studio. Every month the authority is extended by debiting the fee from the wallet. This process may consist of the following steps:
Debiting the amount from the wallet PA1 Confirming the debit through the smartcard and PA1 Extending the authority.
If tale smartcard is now removed between the fist and second steps there will be an inconsistency: The amount is debited but the authority is not extended. Since the smartcard reacher has also not received the confirmation of the debit, its data will indicate that it has neither debited nor extended the authority. Thus the smartcard is unusable and can no longer be restored to a consistent state.
The methods known in the state of the art for writing data to smartcards provide no means of ensuring the integrity of data particularly if the writing process is aborted during writing.